The operator in its current state is based on mouse position and doesnt
make sense to be called from a menu.
(In fact it should be called 'select_linked_pick' internally and a
separate 'select_linked' should be implemented similar to how "Select
Linked" works for meshes, curves etc -- see D7542 for this)
Note: We had the same thing for particles recently:
rBdd9dfadaac9b: remove "Select Linked" from the particle select and
context menu
rB5ca7c85e105d: Particle editmode: add mouse independent "Select Linked"
operator
Fixes T76071
Maniphest Tasks: T76071
Differential Revision: https://developer.blender.org/D7543
536055e1ee